This invention is directed to commercial or residential heat pump systems that provide heating or cooling of a comfort zone, as required, and which can also provide water heating. The invention is more particularly directed towards an improved control arrangement for optimizing the heating of water when the system is in a combined water heating and air conditioning mode.
Integrated heat pumps are often employed to provide heating or cooling, as needed, to a residential or commercial comfort zone, i.e., the interior of a residence, office complex, hospital, indoor recreational facility, or the like. Integrated heat pumps can also be employed to heat water. A heat pump system for air conditioning, comfort zone heating, and water heating is described in U.S. Pat. No. 4,766,734. Systems of this type can have a number of modes of operation, such as air conditioning alone, space heating alone, water heating alone, air conditioning with water heating, and comfort zone heating with water heating. Additional modes, such as a defrost cycle can also be employed. For comfort zone heating and water heating, resistive elements can be employed as auxiliary heating elements for use at times when the heat pump alone cannot produce sufficient heating of the comfort zone or produce enough hot water in the water heater.
During times that indoor space cooling is called for when there is also demand for hot water, the system is operated in a combined air conditioning and water heating mode. The indoor comfort zone air serves as a heat source for water heating. Ideally, to the extend possible the system water heat exchanger should serve as the heat dump for the heat extracted from the indoor comfort zone, so as to make the most efficient use of heat transfer. However, the amount of heat that the water in the water heating exchanger can accept is limited by factors such as its temperature and the amount of heat available. If there is a large cooling load, or if the water temperature is too high, excess heat has to be shed at the outdoor coil. Also, if the water heat exchanger alone is used to cool and condense the compressed refrigerant before returning it to the indoor evaporator coil, unusually high refrigerant pressures may result, and produce high torque conditions and possible damage to the compressor. No combined heat pump and water heating system to date has included means to direct output heat selectively to the water heat exchanger or to the outdoor coil.